I am currently running Mach 4 with Allen Bradley Ultra 3000 AC servo drives. This is open loop from the perspective of the control, but closed loop at the motor. I am curious (educational use only) if there are any control setups that would allow a second position loop to be closed at the control using glass scales mounted on the machine. I could setup the servos as velocity loop only and use a control like CSLabs CSMIO to close the position loop, but I have never seen a Step/Dir controller which allowed you to close the loop.